Several methods in the Card API are asynchronous only. These methods are
asynchronous when Google anticipates some Payment Integrators will
require the following sequence (e.g. due to batch files).

![Async](https://developers.google.com/static/standard-payments/shared/assets/specs/card-fop-v1/async-methods.png)

# What if a Payment Integrator requires synchronous processing?

Rather than support asynchronous and synchronous versions of each method, Google
has opted to only support one version per method. This is intended to make the
launch of new Payment Integrators and ongoing maintenance simpler.

If a Payment Integrator only supports synchronous processing, they can implement
the following sequence. Specifically, they can wait to return ACKNOWLEDGED until
after that have successfully called the fooResultNotification endpoint.

![Async as Sync](https://developers.google.com/static/standard-payments/shared/assets/specs/card-fop-v1/async-as-sync-methods.png)